1. Field of the Invention
This invention relates to linear actuators and particularly to linear electric motors of the stepper type.
2. Description of the Prior Art
Linear electric motors are well known in which a magnetic toothed motor bar and a magnetic armature structure comprising magnetic core and windings interact to produce relative motion in steplike manner when windings are sequentially energized. One such linear stepper motor is described in U.S. Pat. No. 3,867,676, issued to Hi D. Chai and Joseph P. Pawletko on Feb. 18, 1975. In that patent, the linear motor has armature structures that take the form of E-cores. Each E-core has poles with toothed faces coacting with the teeth of the motor bar on opposite surfaces. The E-cores are attached to a rigid frame structure which has rollers on the upper and lower toothed surfaces of the motor bar. The frame and rollers are designed to maintain a fixed air gap between the pole faces of the E-cores and the upper and lower surfaces of the motor bar. In many applications for linear stepper motors, such as for serial printers as described in copending application of Hi D. Chai and Joseph P. Pawletko, Ser. No. 676,584, filed Apr. 13, 1976, precision stepping is required. This type operation requires the alignment of the motors and air gap be very precise and be maintained without deviation under very high mechanical stresses. In the linear motor structure of the abovementioned U.S. patent, the attainment of the desired precise alignment and air gap is achieved only with very costly manufacturing procedures. Tolerance variations in the mounting of E-cores and rollers on the frame members and the parallelism of the upper and lower bar surfaces very easily destroy the desired air gap size and alignments of the E-core pole teeth thereby affecting the precision in the stepping operation of the motor.